Romanesque, a word not coined until the 18th century, is first used to describe the architecture of western Europe from about the 9th to 12th century. It has become applied by extension to other arts, in particular sculpture. But the term remains most appropriate to architecture, where the round arches of Romanesque can easily be seen as what the name implies - a continuation of the Roman tradition.

The round arch is characteristic of much in Roman building - whether in their great aqueducts and bridges, in emperors' triumphal arches, or astride classical columns (as, for example, in the churches of Ravenna).

The capitals of columns, carved with nothing more exotic than acanthus leaves in the classical tradition, provide one area in which the Romanesque sculptor lets his imagination run wild. In abbey cloisters of the period (and abbots are among the main patrons of art in the Romanesque centuries) the tops of the pillars are often alive with vivid biblical scenes or endearingly grotesque monsters, cunningly carved to make the most of the available shape.

This tradition of sculpture, reaching its peak in the 11th and 12th century, is a delight to any but the most stern. But a very strict voice of the time, that of St Bernard, expresses Outrage at these lively frivolities.

The other space regularly made available to Romanesque sculptors, offering a much richer field than the capital of a pillar, is the tympanum - the semicircular expanse of wall between the west door of a church and the arch above it.

A favourite subject for the tympanum is the Last Judgement, particularly in churches such as Moissac or Conques on the pilgrimage route to Santiago de Compostela. The theme vividly reminds the pilgrims of the need for pious devotion; and the numerous characters (particularly the damned and their tormenting devils) provide fine opportunities for the sculptors.

Gothic: 12th - 15th century

Gothic, descriptive now of some of the most sublime creations of the European imagination, begins as a term of abuse. It is used by theorists in the Renaissance to blame the Goths for 1000 years of non-classical architecture - from410 (when Rome is sacked by the Visigoths) to 1419 (when Brunelleschi uses classical motifs on the façade of a foundling hospital in Florence). The term is applied also to sculpture of the same period, much of it found on buildings.

Art historians later recognize a major stylistic division within this long period. The early part becomes known as Romanesque. Gothic, losing any pejorative sense, is reserved for a style which emerges in the 12th century.

The Gothic style, though also used in secular buildings, is most associated with the great cathedrals of Europe. There are certain immediately recognizable characteristics in any Gothic cathedral.

The interior gives an impression of lightness and height, with slender columns framing large tall windows and reaching up to support a delicately ribbed stone roof. The exterior is encrusted with a filigree of delicate ornament, again essentially slender and vertical, made up of a blend of elegant statues, bobbly pinnacles, the skeletal patterns of the stone tracery in the windows, and the open fretwork of flying buttresses.

As with architecture, a sense of lightness and height distinguishes Gothic sculpture from the preceding Romanesque style. Romanesque figures tend to be squat, chunky, angular - particularly when confined to the restricting spaces at the top of a pillar or in the semicircle of a tympanum.

By contrast Gothic sculptures are tall and thin, reflecting the soaring vertical lines of the new style. Alcoves to each side of high cathedral porches are the favourite location for these figures. The abbey church of St Denis is again the pioneer, but the wise and foolish virgins either side of the porch there have been much damaged and restored. Chartres offers the earliest surviving examples of Gothic sculpture.

The sculptures of Chartres: 1150-1220

The earliest porch of Chartres cathedral - the triple entrance in the west façade - introduces Gothic sculpture in its most extreme form. Each of the biblical kings and queens stands on a tiny platform projecting from a tall, thin pillar. To suit their circumstance, their bodies are impossibly elongated within the tumbling pleats of their full-length robes. Yet their faces, by contrast, are realistic and benign.

The result is an effect of ethereal calm, entirely in keeping with Gothic architecture. One of the Chartres sculptors is believed to have undertaken these figures after completing the virgins for the porch of St Denis. So the Gothic style may have been introduced almost in its entirety by Abbot Suger.

The figures in the north porch of Chartres are added half a century later, from about 1195 to 1220. Recognizably in the same style, they are still unusually tall and thin. But instead of being ethereal figures, they are beginning to stir themselves as human beings. Their predecessors in the west porch are aligned with their pillars, as if pinned to them like rare butterflies. The new figures stand more naturally between the pillars. And they look about. They make gestures.

Their creators are beginning to discover a natural way of treating the human figure. Later Gothic sculptors build on that achievement.

From Gothic to Renaissance: 13th - 14th century

An important element of the Renaissance is the rediscovery of the realistic free-standing human figure as sculpted in Greece and Rome. But the emergence of Renaissance sculpture is not nearly as sudden a process as the change involved in Renaissance architecture.

From the time of the north porch of Chartres, in the early 13th century, sculptors create entirely believable people in stone - though attached, invariably, to the walls of buildings. Gradually these figures begin to detach themselves, as if moving towards a more independent existence. The statues liberated in this way are among the masterpieces of Gothic sculpture. But they are also the harbingers of the Renaissance.

The examples usually quoted are mainly from northern Europe. Four figures in the west porch of Reims cathedral, carved between 1225 and 1245, break out of their isolation to relate to a partner. In the right pair the Virgin turns to St Elizabeth in the Visitation; in the left pair she turns to the archangel in the Annunciation.

A secular sculpture from the same period stands high on a platform against one of the walls of Bamberg cathedral. It depicts, in life size, an unknown emperor or king on horseback. This proud horseman is a link (or half-link, being attached on one side) between the free-standing equestrian statues of Rome and of the Renaissance.

Later in the 13th century, from about 1260, stone figures at Naumberg achieve a new degree of humanity. Standing against the wall of the choir, they supposedly depict the founders of the cathedral - dim figures from a distant past. But Ekkehart and Uta stare at the viewer as boldly and believably as if they had only this moment been fixed in stone.

This progression reaches its magnificent conclusion, more than a century later, in a group of Old Testament prophets carved to decorate a well in France.

In 1395 the duke of Burgundy commissions a work from Claus Sluter. He is to provide a scene of Calvary, set on a carved base, to surmount the well of a charterhouse near Dijon. The Calvary has been destroyed, but the base survives - surrounded by six sturdy Old Testament prophets. These figures, carved in 1400-1405, stand as free and as convincing as anyone possibly could whose eternal task is to stand guard round a well (the Well of Moses). With these prophets the naturalistic side of the Renaissance makes its appearance in the north, several years ahead of Donatello in Florence.

The classical theme of the Renaissance is more specifically Italian. But that too is anticipated a good century and a half before Donatello.

Nicola and his pulpit for Pisa: 1259

In the mid-13th century the cathedral authorities in Pisa commission a pulpit for their baptistery. The sculptor is Nicola, from southern Italy but now living in Pisa and so known as Pisano. In his youth he may have been influenced by the classicizing ideas of the emperor Frederick II, who encourages architects and artists in his realms to look to antique models.

Certainly this is what Nicola does when designing the reliefs for his Pisa pulpit, completed in 1259. There are plenty of ancient sarcophagi around to inspire him. His Virgin Mary, in scenes such as the Nativity or the Adoration of the Magi, is a powerfully sculpted figure. But she looks for all the world like a Roman matron.

Nicola follows his success in Pisa with another pulpit in a similar style for the cathedral in Siena, completed in 1268. And his son, Giovanni Pisano, later produces a magnificent pulpit for the cathedral in Pisa, more than rivalling his father's in the baptistery.

These later pulpits of father and son have a more expressive quality. They avoid the direct, even blunt, borrowing of antique forms seen in the Pisa baptistery pulpit. Such an evident interest in the classical past will not reappear until Brunelleschi. But Nicola demonstrates that in this matter the early masters of the Renaissance cannot claim absolute priority.